This invention relates generally to headgear suspension systems and in particular to a selectable sizing apparatus which permits the use of a single size rigid helmet with a variety of head sizes and contours and for additionally providing cooling and ventilation within the rigid helmet and stabilization between the rigid helmet and a flexible helmet positioned on the wearer's head.
Personnel engaged in aircraft flying activities such as pilots and crewmembers often require the utilization of headgear for protection against head injuries and also for incorporation of various electronics such as communications and automatic targeting systems. Heretofore the varying contours of human heads required to be fitted with a helmet necessitated the storage and application of a wide variety of corresponding rigid helmet sizes and corresponding internal flexible helmets which are customarily worn in intimate contact with the head and which are conventionally attached to the rigid helmet by a plurality of appropriately positioned suspension straps and snap fasteners. In order to provide a better form fit about the wearer's head and the internal flexible helmet, the outer rigid helmet is conventionally lined and padded with a layer of foam-like material which, although providing a better fit to the user, inhibits airflow and permits slippage between the outer and inner helmets. Modern aircraft weapon systems, in one example, incorporate a visual target acquisition system which provides a target sight on a visor attached to the rigid helmet and which sight is initially aligned and boresighted before take-off with the rigid helmet in place on the pilot's head. Such systems require that the movement of the outer rigid helmet be carefully coordinated with the movement of the pilot's head in order to insure target accuracy and continued reliability of the target acquisition system during flight operations.